1. Field of the Invention
The present invention relates generally to a fluid pump driven by an engine of a motor vehicle and, more particularly, to such a fluid pump incorporating a continuously variable speed converter therein.
2. Description of the Prior Art
It is desirable to maintain constant the flow volume of fluid delivered from a fluid pump driven by an engine of a motor vehicle to power actuators, such as power steering. For this purpose, there has heretofore been utilized a flow volume control valve which serves to cause a surplus volume of fluid to flow back to a suction area of the pump when the same delivers pressurized fluid beyond a predetermined volume. However, the provision of the control valve does not effect decreasing the flow volume of fluid delivered from the pump itself, thus resulting in great power consumption of the engine by the pump. Particularly, the power consumption by the pump is extreme when great load acts on the pump. This not only brings about engine power loss to increase fuel costs, but also significantly increases the temperature of the working oil to accelerate deterioration in the quality of the working oil.
In order to solve these drawbacks, there has also been suggested an improved pump drive mechanism, in which, as disclosed in U.S. Pat. No. 3,653,272 to M. H. Scheiter, a continuously variable speed converter is utilized to transmit the driving power of an internal combustion engine to a fluid pump at various output/input speed ratios. The mechanism is further provided with an "internal sensing" ratio control means which senses changes in fluid force, reflecting changes in input speed, so as to control the output/input speed ratio. Since the change in fluid force is effected under the action of centrifugal force when a housing containing a predetermined volume of fluid is rotated and since the centrifugal force changes in proportion to the 2nd power of the rotational speed of the housing, the output/input ratio does not have a linear proportional relation with the rotational speed. Accordingly, even using the mechanism, the volume of fluid from the pump cannot be accurately maintained at a constant value.